The invention relates generally to method and apparatus used to cast molten materials. More specifically, the invention relates to a method and apparatus that includes a funnel insulated with a phase-change marerial used to cast explosives, especially explosive projectiles. The invention takes advantage of the latent heat of fusion of the phase-change material to maintain the funnel and projectile neck at an elevaled tempaerature during the casting and cooling process in order to keep the funnel and projectile neck open.
A common method for manufacturing explosive projectilies involves pouring molten explosive material into a body casing. Typically, a funnel is used to help guide the molten explosive material into the projectile body. Explosives such as trnitrotoluenen (TNT) and composition B (a mixture of TNT and cyclotrimethylenetrinitramine (RDX) contract as they cool and harden into a solid. This contraction can cause gaps or porosities in the final product. These gaps are undesirable and can cause problems such as premature explosion in the gun barrel.
One strategy for avoiding the gaps is to overfill the projectile body during the initial pour of the molten explosive with the excess explosive being contained in the funnel immediately after the pour. If the explosive in the funnel is kept in a liquid state, it can feed into the projectile body, as the explosive in the projectile body hardens and contracts, thereby filling-in the gaps that otherwise form. In order to prevent the molten explosive from cooling too quickly and solidifying, it is known to insulate or heat the funnel.
If the funnel surface gets too cool, it can cause the molten material to harden and block the funnel. If the funnel surface gets too hot, that can cause problems as well. The high temperature heating surfaces present a safety hazard to users if the user skin would come in contact with the heated surface. Additionally, if the heated surface gets too hot, it can present a risk of explosion.
Funnels that are merely heavily insulated, but not provided with any source of heat, typically do not keep the funnel open for a sufficient time to prevent defects in the casting. Funnels that are provided with a heat source, such as hot water or steam oven panels typically will keep the funnel open for a sufficient period of time to allow for a complete casting. However, such methods of heating the funnels have a high initial cost and a high operating cost. If the temperature of the funnel surface is not carefully controlled, it may heat the molten explosive above the desired temperature. Another option is to preheat the funnel in an oven. The primary difficulty with this method is that the funnel must be prohibitively massive in order to retain enough heat to keep the funnel open for the required length of time. It can also be difficult to control, or even verify, the temperature of the funnel during the process when using this method. Additionally, because it is necessary to heat the funnel above the melt temperature of the explosive, this method can lead to heating the molten explosive above the desired temperature during the beginning of a pour.
An additional method of heating the funnels uses forced air. This also results in high costs because it requires the control of airflow to multiple ovens. It also requires proper ventilation to remove explosive fumes that may be carried in the heated air. Finally, the air temperature must be above the melting point of the explosive, and therefore tends to heat the molten explosive above desired temperatures.
Therefore, there exists a need for a method and apparatus that permits the casting of explosive projectiles that maintains the funnel open for a sufficient amount of time to permit a highly quality cast, but does not heat the molten explosive above desired limits. Preferably, the apparatus will not have a high initial cost or a high operation cost, will be safe to use, and will be consistent and reliable.
The present invention satisfies the above identified needs.
The present invention is directed to an insulator and funnel for use in pouring explosive projectiles. The funnel has a sloping funnel surface in thermal contact with a reservoir in the insulator. The reservoir contains a phase-change material. The phase-change material has a melting point that is higher than the melting point of the explosive material. Preferably the phase-change material is also in thermal contact with a top, or neck portion of the projectile body. The phase-change material is preheated to a temperature sufficient to melt the phase-change material. A molten explosive material is poured through the funnel into a projectile body. As the phase-change material changes from a liquid to a solid, the latent heat of fusion of the phase-change material maintains the sloping surface of the funnel and projectile neck at a near constant temperature that is warm enough to permit the molten explosive material to flow through the funnel and projectile neck for a sufficient amount of time to supply molten explosive into the projectile body as it cools, shrinks, and solidifies.